In a statement to police in 2006 Walter Litvinenko told how his son was struggling to speak when he visited him in hospital but accused Russian president Vladimir Putin over his death - a claim the Kremlin has always denied.

Vladimir Putin

Mr Litvinenko was said to have told his father: "Daddy, Putin has poisoned me."

Inquiry chairman Sir Robert Owen criticised Mr Kovtun and Russian authorities. He said: "This unhappy sequence of events drives me to the conclusion either that Mr Kovtun never in truth intended to give evidence and that this has been a charade.

"Alternatively, if he has at some stage been genuine in his expressed intention to give evidence, obstacles have been put in the way of his doing so.

In a statement given to the Inquiry, Mr Kovtun claimed he had ended up in the bar at the Millennium Hotel with Mr Litvinenko and Mr Lugovoi "completely by chance".